1. Field of the Invention
The present invention relates to a thread end holding unit of a sewing machine.
2. Description of the Prior Art
A thread end holding unit of the sewing machine has the function of cutting off a needle thread and a bobbin thread under a processed cloth upon completion of sewing the processed cloth, by drawing the thread end at the upper side of the processed cloth, and holding the thread end thereby preventing the thread end from being entangled in a form similar to a bird's nest at the rear portion of the processed cloth.
A prior art thread end holding unit is disclosed in Japanese Utility Model Laid-Open Publication No. 61-157487. This unit employs a needle thread gripping puller provided at the side of an arm of the sewing machine which is driven to reach a catch position or a return position. The puller has a hook portion for catching the needle thread extending downward from the needle toward the processed cloth in the catch position and holding it in the return position. A holding member having a base end portion fixed to the side of the arm of the sewing machine and a tip end portion for contacting the needle thread gripping puller to press and hold the thread end of the needle thread caught by the hook portion at the time when the needle thread gripping puller takes the return position.
However, this prior art thread end holding unit was found to be subject to an undesirable condition wherein the thread end of the needle thread caught by the hook of the needle thread gripping puller is pressed and held by a single holding member. The rigidity of both the needle thread gripping puller and the holding member must be increased to increase the holding force of the needle thread. Inasmuch as the needle thread is pressed and held by the friction force generated at the narrow portion between the needle thread gripping portion and the holding member, it is easy for the needle thread to be dropped.
Japanese Utility Model Laid-Open Publication No. 62 -109079 discloses a structure wherein the needle thread cutting unit has a cutting knife for cutting off a thread end of the needle thread at the side of the processed cloth held by the thread end holding unit at the same time of starting the sewing of the processed cloth. This arrangement is subject to erroneous performance of the needle thread cutting unit. This problem arises because the needle thread cutting unit employs a structure for cutting off thread end of the needle thread held by the thread end holding unit during the movement of the processed cloth. The thread end holding unit causes a tension in the thread end of the needle thread which dulls the sharpness of the blade cutting the needle thread. When the knife is so dulled, the thread end holding unit must apply a strong holding force in order to maintain a suitable thread cutting operation.